1. Field of the Invention
The subject invention relates to valves suitable for use in fuel supply systems and, more particularly, flow dividing valves having a zero flow output condition.
2. Description of the Prior Art
For many years, gas turbine engines have used fuel supply systems that separated fuel flow into a primary flow and a secondary flow. Such engines are generally designed to use the primary flow for starting and at low power requirements. At higher power requirements, the engine requires that the primary flow be supplemented by the secondary flow.
Some fuel supply systems known in the prior art divided fuel flow into primary and secondary flow paths, but had no operational mode in which fuel flow to the engine was completely off. Such fuel supply systems typically incorporated flow control valves such as described in U.S. Pat. No. 3,727,636 and had two operational modes; one in which only a primary output flow was provided, and one in which both primary and secondary output flows were provided. Thus, at all times, when fluid was provided to the input port of the fuel supply system, at least one output flow would result.
For certain applications where a zero output flow condition was required, a shut-off mechanism was placed adjacent the input to the fuel supply system. For example, for gas turbine engines used on aircraft, a manifold leakage control valve was placed adjacent the inlet to the fuel nozzle. When the engine was off, the manifold leakage control valve shut off flow to the fuel nozzle. This prevented fuel flow from flowing through the primary circuit of the fuel nozzles and accumulating in the combustion chamber manifold.
While such prior art arrangements afforded a shut-off condition for the output flow of the fuel supply system, they require the use of at least two valves and resulted in increased complexity, maintenance and expense for the overall system. Thus, there was a need in the prior art for a single valve that could divide an input flow into at least two output flows and that also had a zero output flow condition such that a flow dividing valve could replace prior art fuel supply networks without need for any additional shut-off mechanisms.